Chiral diphosphorus donor ligands have been found to be valuable ligands for catalytically active metal complexes which are used in homogeneous catalysis for the enantioselective hydrogenation of organic compounds. Fields of use are the preparation of intermediates or active compounds, for example pharmaceuticals, pesticides, flavors or fragrances.
In enantioselective hydrogenation, these diphosphorus donor ligands are used together with suitable noble metal complexes.
Organometallic Ru compounds used in these hydrogenations are, for example, [Ru(COD)Y2]x, [Ru(NBD)Y2]x, [Ru(aromatic)Y2]x or [Ru(COD)2-methyl-allyl)2] (where X=2; Y=halide, COD=1,5-cyclo-octadiene, NBD=norbornadiene, aromatic=for example p-cumene or another benzene derivative).
EP 1622920B1 discloses transition metal complexes having ferrocenyldiphosphine ligands. Complexes having specific P-P coordination of the phosphine ligands are not described.
Ru complexes having (P-P)-coordinated diphosphorus donor ligands are known from the literature.
M. Sato and M. Asai (J. of Organometallic Chemistry 508 (1996) pp. 121-127) describe permethylcyclopentadienyl-Ru(II) complexes having dppf, BINAP and DIOP ligands. As a result of the permethylcyclopentadienyl radical, these complexes are very stable; use for catalytic hydrogenation is not described.
C. Standfest-Hauser, C. Slugovc et al. (J. Chem. Soc. Dalton Trans., 2001, pp. 2989-2995) report cyclic Ru(II) semisandwich complexes which likewise have a cyclopentadienyl ligand and also chelating phosphino-amine ligands. These complexes contain a cyclopentadienyl ligand (“Cp ligand”) and are not very suitable for use as catalysts for homogeneous asymmetric hydrogenation. They are normally used in a specific catalysis reaction (namely transfer hydrogenation), with the Cp ligand stabilizing the catalyst and having to be coordinated to the metal during catalysis.
J. B. Hoke et al. (J. of Organomet. Chem., 1993, 455, pp. 193-196) describe ruthenium complexes in which BINAP ligands form a seven-membered ring with the Ru. The complexes contain one cyclopentadienyl group. They are very stable but display little activity in catalytic hydrogenation and some of them are unselective since the Cp ligand is bound very strongly to the metal.
P. S. Pregosin et al. (Organometallics, 1997, 16, pp. 537-543) have reported a ruthenium complex which bears the MeO-BIPHEP ligand and additionally has a cyclooctadienyl radical. The complex can be prepared only by means of a complicated process and is very air- and moisture-sensitive. Use for catalytic hydrogenation is not described. A similar complex bearing the BINAP ligand has been described by S. H. Bergens et al. (Organometallics, 2004, 23, pp. 4564-4568). An acetonitrile complex was isolated in the synthesis and this is not very active in catalysis.
A. Salzer et al. (Organometallics, 2000, 19, pp. 5471-5476) have reported the preparation of a seven-membered BINAP-ruthenium complex from a (bispentadienyl)Ru compound as starting complex.
D. A. Dobbs et al. (Angew. Chem. 2000, volume 112, pp. 2080-2083) describe a ruthenium-containing precatalyst having a P—P-coordinated DuPhos ligand. The cyclic compound is an Ru hybrid species and has an uncharged cyclooctatrienyl ligand. It is very sensitive and was prepared in a glove box (inert gas: Ar containing <1 ppm of oxygen). Such sensitive compounds are not very suitable for industrial use.
WO 00/37478 describes transition metal complexes which have a metal atom of transition group 7 or 8 and in which both P atoms of a diphosphine ligand are simultaneously coordinated to the central atom, but the complexes are neither isolated nor characterized. No preparative method is described; rather, the complexes are generated by combining the ligands and the appropriate transition metal salts in the reaction solvent shortly before use (“in-situ”). These in-situ processes are prior art. Few studies have hitherto been carried out on the structure of the metal complexes generated in-situ; the corresponding complexes were not isolated but instead used directly in the reaction mixture for homogeneous catalysis, in particular for catalytic hydrogenation. The mechanistic studies are carried out using model systems which do not correspond to the real active catalytic species.
U.S. Pat. No. 6,455,460 describes a ruthenium catalyst obtainable by a process which comprises putting together an appropriate Ru(II) complex, a chelating diphosphine and an acid comprising an non-coordinating anion. The reaction is performed under an oxygen-free atmosphere.
Disadvantages of the catalytic hydrogenation processes described hitherto and the catalysts used therein are, in particular, the low reactivity, the low enantioselectivities and a high consumption of noble metal-containing catalyst, i.e. a low “substrate/catalyst” (S/C) ratio. Furthermore, long hydrogenation times are required. In addition, many of the complexes described are difficult to synthesize, are air-sensitive and are not very suitable for industrial use.